Shell molding composition comprising thermosetting phenol-formaldehyde resin, coating agent, and sand, and process for making same



Nov. 10, 1959 F w. LESS ETAL 1 2,912,402

SHELL MOLDING COMPOSITION COMPRISING THERMOSETTING Pl-IENOL-FORMALDEHYDERESIN, COATING AGENT. AND SAND, AND PROCESS FOR MAKING SAME Filed Sept.8. 1954 INVENTOR z a w United SHELL THERMOSETTING PHENOL FORMALDEHYDERESIN,= COATING AGENT, AND SAND, AND PROCESS FOR MAKING SAME ApplicationSeptember 3, 1954., Serial No. 454,702

9 Claims. c1. 260-30.6)

This invention relates to the making of molds and cores. Morespecifically it refersto a new composition and method therefor for usein making such molds and cores.

In FIAT Final Report No. 1168, entitled, The C Process of Making Moldsand Cores for Foundry Use, by William W. McCulloch, Oflice of TechnicalServices, May 30, 1947, there is described a process for making foundrymolds which utilizes a mixture of sand and a thermosetting resin,specifically a mixture of phenolic resins and hexamethylene tetramine.More recently a variation of the process has been developed which isbased upon the traditional method of blowing sand cores by means of anair pressure type of blowing machine. In this new method a mixture ofsand and phenolic resin is placed in the charge chamber of acore-blowing machine, and the mix is injected under air pressure into anenclosed heated pattern. The mixture then fills the cavity underpressure and is later cured with the applicat-ion of heat, so that thesurfaces of the mold conform to the interior surfaces of the patterncavities.

There are many advantages to be gained by utilizing the core blowingmethod in conjunction with the shell mold process. First, internal moldsor cores can be produced as well as external molds' In the Croning ordumping process only external molds can be readily formed. Second, shellmolds may be produced having a uniform thickness since the sand mixtureisblown into a confined or predetermined cavity. In the Croning' ordumping process the thickness is determined by the dwell time andtemperature conditions, which are difficult to control precisely. Third,both surfaces of the mold can be contoured in the blowing process. Inthe Croning process only the sidein direct contact with the heatedpattern can be contoured, and the back part must remain irregular sincethe blown mold is formed in a confined space, a mold possessing 100%definition is produced. Fourth, the amount of the materials'needed forproducing the core or mold may be more readily predetermined in theblowing method since the thickness of the mold or core is known inadvance. In the Croning process this is not possible as it is impossibleto predetermine the exact temperature or dwell time. Fifth, the internalmolds or cores may be made hollow by first filling the pattern cavityand then allowing the unused portion to run off. Sixth, since externalmolds produced by the blowing" process can be formed having apredetermined contour on the reverse side, they can be adapted to thepermanent type of mold support. This enables use to be made of positivemethods to back up the mold, thus preventing mold fracture during thecasting operation.

Other advantages of the blowing process can be seen when the limitationsof the Croning process are considered. For instance, in the Cron-ingprocess, after the mix has been in contact with the heated patternsufficiently long to form a mold of desired thickness, the pattern andthe excess sand are inverted so that the excesssand can fall ofl. Atthis point there is a tendency MOLDING CQMPQSITION COMPRISING Patent forthe mold to fall off the pattern. To prevent this, special resins areused which are less fluid than would normally be desirable. Thefall-oiiof the mold is thus prevented, but the use of a resin that has a lowerfluidity results in a finished mold that has less strength than one madewith a more fluid resin. When molds are pro-' duced by the blowingprocess, this problem does not exist since the mold is completelycontained in the pattern until it has completely cured. Since there isno fall-off problem, resins which are more fluid can be used which inturn produce stronger shellmolds. 7

Another advantage of the blowing method resides in the fact that themethod may be used for preparing molds for stack pouring, since bothsurfaces of the mold may be contoured and cured. Stack molds consist ofa cope patterned on one surface and a drag for the succeeding mold onthe other surface. The molds are then assem bled in groups and may bepoured with a common sprue. In the dumping process only one surface maybe con toured. As a result it is impossible to produce molds directlyfor stack pouring.

A saving in time also results through the use of the blowing methodsince patterns may be filled almostinstantaneously and removed from theblowing machinery into a furnace to be cured. In the dumping process thesand mold mixture must remain in contact with the pattern for asufiicient length of time to form a mold of desirable thickness beforethe excess sand is dumped oil and the mold removed to be cured.

These many advantages of the blowing process at first could not berealized, since the material used in the dumping or coating process wasnot completely suitable for use in blowing shell molds or cores. Themolding material as used in the'original coating process consistedof amixture of sand and finely powdered resins. This mixture was made byplacing sand and resin containing admixed hexamethylene tetramine into amixer and mixing it thoroughly for several minutes. However, since theresin is very finely ground, a problem has always existed in that thefinely ground resin tends to disperse through the air when the materialis manipulated, creating considerable clouds of dust and destroying theuniformity of the mixture. Our prior applications, Serial No. 220,700and 220,704, filed April 12, 1951, both now abandoned (said applicationsSerial No. 220,700 and 220,704 being themselves continuations-inpart ofour application Serial No. 135,316, filed December 27, 1949, nowabandoned), of which this application is a continuation-'in-part,disclose the use of a liquid additive to prevent the resin from beingsegregated. Although this material in the proportions disclosedandclaimed in the aforementioned application aids materially in decreasingthe amount of resin dust from blowing around, it still does not producea material that is entirely suitable for use in the blowing process. Itwas found that when this mix is used the resin still segregates from thesand to some degree during the blowing process. I

When the mixture is carried in the air stream some of the resin becomesseparated from the sand particles and forms low and high resinconcentration areas Within the mold, resulting in-the production of aweak mold. In

the areas Where the resin is dense, the mold gases can- In attempting tosolve this problem it was discovered that if a continuous resin coatingcould be applied to each sand particle, there would be no segregationtaking place during the blowing process. In addition, it was discoveredthat a lower percentage of resin could be used in a mixture which wouldstill give tensile strength comparable to molds made with uncoatedmixtures containing greater percentage of resin.

A number of methods for producing the uniform coating upon the sandparticles have been tried by various workers in the field with more orless success. One method consists in mixing the sand with a solutionformed by dissolving powdered resin in a solvent, and then driving offthe solvent, generally with the addition of heat. One disadvantage ofthis method is that it is difficult to get the solvent out of themixture after the mixing process is complete. The solvent evaporatesrapidly at first, but, after the viscous stage is reached, theevaporation is accomplished only with extreme difiiculty. Anotherdisadvantage of this process is that there is a tendency for the resinto be pulled olf the sand particles. This results in a nonuniform mix.Another disadvantage is that the mixture formed remains quite tacky. Thecured molds formed have low tensile strength because the resin coatingdoes not adhere well to the sand particles.

The second method uses a series of steps very similar to the processused for producing grinding wheels. A liquid resin is first mixed withsand. Then the powdered resin is added and partially succeeds in dryingthe mixture. The main disadvantage with this method is that the mixturehas green strength, that is, it is quite sticky, lumps, and forms apermanent set when pressure is applied. This makes it veryunsatisfactory for use especially in the blowing process where afree-flowing mixture is required. In addition the resin content must benecessarily high in this method in order to achieve suitable tensilestrengths in a mold.

The third method, in contrast to the two mentioned above, is acold-coating method and consists of mixing the sand with a liquid resinand a small amount of solvent. The material is then dried by addinghexamethylene tetramine and wax. The disadvantages of this method arethat this material also has green strength and packs, making itunsatisfactory either for normal shell mold use, or for shell mold orcore blowing.

The fourth method consists in mixing the sand and the liquid resintogether at a high temperature, and then adding hexamethylene tetramineto advance the resin. This method is difiicult to accomplish andrequires expensive equipment for heating the mixing ingredients whichmost foundries do not have available. Another disadvantage is that,during the period When the hexamethylene tetramine is added, the resinis continuously being advanced. Therefore, elaborate equipment isrequired to control the process in order to get a material which isadvanced to the same degree as any previous batch which has been made bythis process.

The fifth method consists in mixing sand with a fused resin at hightemperature, forming a coating, and then cooling the mixture andpulverizing it. This method also requires expensive equipment and istime-consuming and costly.

It is an object of the present invention to provide a composition whichis suitable for the manufacture of shell molds and cores by means of theair-blowing process.

It is a further object of this invention to provide such a compositionwhich can be rendered uniform and which will remain uniform throughoutthe blowing process and which does not require the use of special andcomplicated mixing equipment.

It is another object of the invention to provide such a compositionwhich can be produced and used without causing formation of dust, sothat the danger of health and safety involved in the manufacture of theknown mixtures is eliminated.

Still a further object of the present invention is to provide a methodfor preparing a shell mold composition wherein each sand particle issubstantially coated with resin, and wherein there remain essentially noresin particles in the mix which might segregate when blown about by theair currents.

Further objects and advantages of the invention will appear more fullyfrom the following description, especially when taken in conjunctionwith the accompanying drawings which form a part thereof.

In the drawings:

Fig. 1 shows on a greatly enlarged scale a composition of the typeproduced by the normal admixing of sand and resin;

Fig. 2 shows a mix prepared in accordance with our prior applicationsSerial Nos. 220,700 and 220,704; and

Figs. 3 and 4 show compositions prepared in accordance with the presentinvention.

In our pending applications, a method has been disclosed and claimed foravoiding some of the disadvantages of a dry sand and resin mix in whicha liquid adhesion agent is added to cause the resin particles to clingto the grains of the sand. This process contributes materially ineliminating the dust problem. However, this material as disclosed in theprior applications still was not entirely satisfactory for use in thesand blowing process, since the high degree of turbulence in the airstream succeeded in segregating some resin even from this mix to such anextent that the remaining mixture did not always form satisfactory blownmolds and cores.

It has now been discovered that sand particles may be substantiallycompletely coated with a film of resin without any external applicationof heat by incorporating into the mix a specified amount of a properlyselected liquid coating agent, if the ratio of coating agent to resin iskept within well defined limits.

The compound used as the coating agent may in many cases be the samecompounds as disclosed in our pending applications Serial Nos. 220,700and 220,704.

The liquid used in our co-pending application was used in a ratio ofless than 1:10 to the weight of resin. It was therefore unexpected tofind that if the ratio Was increased to one greater than 1:10, theliquid would act as a coating agent and effect a susbtantially uniformcoating of resin surrounding each sand particle which would notsegregate from the mixing during physical manipulation. It has beenfound that when the ratio of coating agent to resin lies in the range of1:10 to 4:10 a resin coated sand is produced by the present processwhich is satisfactory for shell and core blowing and which is equallysatisfactory for use in the Croning or dumping process. Where the ratiois lower than 1:10, an effective coating will not be produced. Where theratio is greater than about 4:10, although a coating will be produced,the resulting mixture is somewhat too sticky and has green strength, sothat it is no longer satisfactory for use in the blowing process.

The liquid used as a coating agent should possess certam properties.First it must have a relatively high boiling point in order to producemixes which have good stonng properties under normal room conditions.Second, it must exhibit a limited solubility in the resin used. It mustnot be a very good solvent for phenolic resins, nor can it be a completenon-solvent at room temperature. It was found that some liquids have toohigh a solubility in the resin used, so that a mix made therefrombecomes sticky, cakes, and fails to flow freely when used in the moldblowing process. On the other hand, there are those compounds which arenot sufiiciently soluble in the resin, resulting in the complete absenceof any coating action. Between these two groups lies a third groupcomprising a large number of compounds which are slightly soluble in theresin and which soften it to the extent only that the resin is able toform a coating about each sand particle and adhere thereto.

In -view of the fact that the present invention depends upon thephysical properties of the various compounds used ascoating agentsrather than any chemical or functional property, and since the operativematerials do not appear to fall into any particular chemical class ofcompounds based on the functional groups, it became necessary toformulate a method for defining which compounds were operative and whichwere not, based on their physical properties. It .was found that thecoating agent first of all had to exhibit those properties listed above.It was then found necessary to work out a method to define empiricallywhat compounds exhibited the desired solubility in phenolic resins suchas to be operative in coating the resin upon sand, andyet which was notso soluble that it produced a sticky mixture. The following method wasdeveloped.

First, a phenolic resin was prepared to use as a reference standard. Forthis purpose a novolac type of resin was chosen, that is, one which didnot have sufficient formaldehyde contained therein to form athermosetting resin upon application of heat. It was necessary to usesuch a resin in order to prevent any advancement of the resin during thetesting. The resin was prepared by reacting 0.8 mol of formaldehyde with1 mol of phenol using sulfuric acid as a catalyst in the usual methodfor making a phenol formaldehyde novolac resin. The resin had a meltingpoint of about 80 C. shrink and about 90 C. clear. The referencestandard resin was'then mixed with measured amounts of the variousagents to be considered for use as coating agents and the mixture washeated until a uniform product formed. The melting points of theseresulting mixtures were then measured by each of two different methods,and the melting point depression produced by the addition of each agentwas determined. -The various agents were then utilized in the coatingprocess and tests made of the resulting mix to determine the tensilestrength of the various finished molded materials. The table listedbelow shows the various compounds used as coating materials and theresulting melting point produced when mixed with the standard referenceresin.

MELTING. POINTS In the tests resulting in the data listed above 16% byweight of each coating agent based on the resin was mixed with thestandard reference resin. The resin used in every case was a novolacresin as described above. The mixture was heated until the resin melted,and then the liquid resin and the coating agent were mixed togetheruntil a homogeneous liquid resulted. This was then allowed to cool andthe melting point of the resulting mixture was determined. The dataabove show the resulting melting points as determined by two differentmethods, the shrink method and the clear method. The melting pointdeterminations were made in a capillary tube. The shrink temperature isthe temperature at which the powder begins to shrink away from the tube.The clear temperature is the temperature recorded at the point where theopaqueness of the material within the capillary tube disappeared andwhere the transmitted light through the capillary tube indicatedclarity.

The values for the tensile strength were determined by mixing with sandabout of one percent (0.4%) of the coating agent and 2 /2% of acommercial shell mold powdered resin such as Durez 17060 (aphenolformaldehyde resin with 10% of hexamethylenetetramine). Theprepared mix was then made into shell molds both by the dumping processand by the blowing process, and

the tensile strengths recorded. 7

From the above tests it was found that'materials which are relativelyinsoluble in phenolic resins like kerosene did not even form ahomogeneous medium when mixed with the standard reference resin. Thismaterial also was not sati'sfactoryin coating the resin upon the sandparticles. Tricresylphosphate was very satisfactory in coating the resinand produced molds having satisfactorytensile strengths. Materials suchasdirnethylformamide and glycerine, although they succeeded in coatingthe" resin upon the sand, produced sand-resin mixeswhich were rathersticky and which lumped upon the applica tion of pressure. Thesematerials were used only with some difiCUItY. Materials which were moresoluble in phenolic resin and as a result depressed the melting pointsto a greater degree than glycerine were found to be unsatisfactory forproducing coated sand for the shell mold processes described above.

From the results of the tests outlined above, it was determined thatthose liquidswhich when mixed in the proportions as outlined above witha standard reference phenolic novolac which melts at about C. by theshrink test or C. by the clear test will depress the melting point notmore than about 30 C. are satisfactory for coating resins in the processof the present invention. Those materials which, when tested in the sameway produce a melting point depression greater than about 30 C. havebeen determined to be unsatisfactory for the process. Materialscompletely incompatible with phenolic resins are also, of course,unsatisfactory.

The term standard reference phenolic resin having a melting point ofabout 80 C. as used in the claims refers to a novolac resin of the typedescribed above.

In order to accomplish a satisfactory coating of the sand, the ratio ofthe coating agent to the powdered resin must be controlled within ratherclose limits. In order to get any coating at all, it is generallynecessary that at least 1 part of coating-agent to l0parts of powderedresin by weight must be used. The ratio of the coating agent to resinmay be increased until the value reaches 4 parts of coating agent to 10parts of resin, beyond which point the resin-sand mixturev formed willbe too wet and sticky for satisfactory shell blowing.

The amount of resin usually used based on thetotal mixture generally isin the range of 1% to 10%. Mixes containing less than 1% resin do notform molds with satisfactory tensile strengths. Mixes containing greaterthan 10% resin may be used but become commercially uneconomical. Therange of the coating agent generally varies from to 4% by weight basedon the total mixture.

Although individual compounds have been described for use as coatingagents, it is to be understood that mixtures of two or more compounds,which mixtures themselves exhibit the properties described aboveasdesirable, may be used.

The process of the invention is generally carried out by placing thesand in any one of several types of mixers commonly used in foundrywork. Examples of these are: the Beardsley-Piper speed muller and theSimpson muller. The coating liquid is then slowly added to the sandwhile the mix is kept in motion. After approximately five minutes, theresin is added, and mixing is continued for a period of from 5 to 30minutes depend ing on practical considerations. When a mixer has notbeen used for a considerable period of time and is therefore at roomtemperature, the first coating run may require a greater mixing periodthan when the mixing equipment has attained'a higher than roomtemperature due to the heat resulting from the friction of mixing fromthe past operation. After several'runs, mixing may be accomplished in asshort a period as 5 minutes. After :the necessary mixing period has beencarried to 7 completion, the sand is removed from the mixer and then canbe utilized in the moldmaking operation.

The effects of the process of the present invention upon sand mixes maybe illustrated by means of photomicrographs of the mixtures,representations of which appear in Figs. 1 to 4. Fig. 1 shows a mixtureof sand and resin such as is generally used for the Croning process. Itwill be noted that the resin and the sand exist completely apart fromeach other and that the resin is free to segregate when any motion ofthe mixture takes place. Fig. 2 shows a mixture such as prepared by theprocess disclosed in our co-pending applications Serial Nos. 220,700 and220,704, which disclose a process for preparing a molding mix in whichthe dusting problem has been considerably alleviated. it will be seenthat a large part of the resin loosely adheres to the sand particles,but that considerable resin remains apart from the sand grains and isfree to segregate. In this coating process a coating agent to resinratio of less than 1 to was used.

Fig. 3 is a representation of a photomicrograph taken of a mixture madeaccording to the present invention in which 0.4% of coating agent andabout 2 /2% to 3% of resin were used. As seen through the microscope,there are no discreet particles of resin visible in the field,indicating that the resin must have formed a continuous coating abouteach sand particle. This is the optimum type of mix to be obtained bythe process of the present invention and results in shell molds andcores having maximum strength. The mix thus illustrated was prepared ina Beardsley-Piper speed muller. When this same mix is prepared in amixer such as the Simpson muller, where the energy and speed of rotationare not nearly as great as that of the Beardsley-Piper muller, a mix asshown in Fig. 4 results. Here the sand particles are substantiallycoated with resin, but there still remain discreet particles visibleWhich adhere to the surfaces of the sand particles. Almost no resinparticles are shown in the field indicating that the mixture will not besubject to segregation of the resin particles during motion.

As used in the present application in both the specification and claims,the term coated sand applies to material as illustrated in either ofFigs. 3 and 4 depending on the type of mixing equipment used. Eithertype is satisfactory for use in either the blowing process or thedumping process. Mixes may be made in the slower type of mixer such asthe Simpson muller having the completely coated composition of Fig. 3 byincreasing the mixing period and thus developing more internal heatduring the coating process.

The relative amounts of the coating agent and the resin used depend to alarge extent upon the type of sand used to make the shell mold mix. itis generally customary, because of high transportation costs, forfoundries to use that type of sand that is found in their locality. Itis therefore necessary to alter proportions somewhat to adapt theprocess of the present invention to fit the conditions determined by theproperties of the local sand. For instance, with a sand having largegrains and a smooth round surface, such as Wedron No. 60 sand as sold bythe Wedron Silica Company, as little as 0.1% to 0.4% of the coatingagent may be used. To maintain the correct coating agent to resin ratioit has been found necessary to reduce the amount of the resin to about1% to 2.5%. However, when a sand containing many small particles withirregular surfaces, such as Juniata, is used, it is necessary to use asmuch as 0.7% to 1.5% of the coating agent in order to accomplish thecoating of the sand. The proper proportions for other sands generallyfall in the range between 0.2% and 1.5%.

The materials which have generally proven to be most useful as coatingagents in practicing the present invention are generally to be foundamong the classes of compounds which are used as plasticizers forvarious resins. Some examples are: tricreslphosphate, triethylphosphate,tributylphosphate and other compounds having similar properties. Inaddition to the compounds listed above, mixtures thereof or relatedcompounds may be used.

Although the present invention has been described mainly in relation toits usefulness in the mold and core blowing process, it is equallyuseful in the Croning or dumping process in that the dusting problem andits attendant health hazards have been completely eliminated and theresulting cured molds generally have a more uniform composition and as aresult a greater tensile strength for the amount of resin used.

The following examples will serve to illustrate the process of thepresent invention and the improvements resulting therefrom:

Example I 300 lbs. of Wedron No. 60 sand were placed in aBeardsley-Piper speed muller. The muller was started and 1.35 lbs. oftricresylphosphate were slowly added. Mixing was continued for about 5minutes, at which time the muller was stopped and 7.5 lbs. of a powderedthermosetting resin, comprising a mixture of phenol-formaldehyde resinand 10% hexamethylene tetramine, powdered to a fineness of 200 mesh wereplaced in the mixer. The mixer was started and allowed to run for 15minutes. At the end of that time the mixture appeared to be free flowingand exhibited no tendency for spreading resin dust. Photomicrographstaken of samples of the mixture showed the complete absence of discreteparticles of resin in the mix. Fig. 3 is a representation of thesephotomicrographs. Because of the absence of any discrete particles inthe mix, it must be assumed that the resin formed a uniform coatingabout each particle of sand. Test molds were made of the material inorder to test its effectiveness in the shell mold process. The moldsmade by the dumping process had a tensile strength of about 263 p.s.i.and those by the blowing process, a tensile strength of about 442 p.s.i.

Example 11 50 lbs. of Wedron N0. 60 sand were placed in a Simpson typemuller. While mixing 0.25 lb. of tributyl phosphate was slowly added.Mixing was continued for approximately 5 minutes, at which time 1.25lbs. of a finely ground mixture containing about 90% phenolformaldehyderesin and about 10% hexamethylene tetramine Were added and mixing wascontinued an additional 5 minutes. After the end of that period, themixture was free flowing and exhibited no tendency for producing resindust. Photomicrographs, of which Fig. 4 is a representation, were takenof samples of the mix and showed no loose resin particles unattached tothe sand particles. Although the sand particles appeared to besubstantially coated with resin, a small number of discrete particlescan be seen adhering to the sand. Despite the lack of a uniform, smoothcoating, the material was found to be as effective as the materialproduced by the speed muller as described in ExampleI and shown in Fig.3. The tensile strength of blown test molds was 439 p.s.i.

It was found that when mixing was continued for a longer period, andwhen the temperature of the mixture was allowed to rise due to the heatgenerated by friction, a mixture could be obtained having the samecompletely coated appearance as the mixture produced in Example I in theBeardsley-Piper speed muller. The above two examples illustrate thedifference in efiect produced by various types of mixers. In general, inorder to achieve a completely coated product in a short time, it isnecessary to use a high speed mixer. However, when such a mixer is notavailable, the slower type may be used to produce a product which,although it does not exhibit a completely coated appearance, issatisfactory for use in the blowing process for making shell molds andcores. Where the completely uniform coating is desired, it may beobtained even with the low speed mixer by increasing the mixing periodand allowing the temperature to rise.

Example III 300 lbs. of Wedron No. 60 sand were placed in aBeardsley-Piper speed muller. The muller wasstarted and 1.4 lbs oftriethyl phosphate were slowly added. Mixing was continued for aboutminutes, at which time the muller was stopped and 7.5 lbs. of thethermosetting resin described above were placed in the muller. Themuller was started and allowed to run for 15 minutes, at the end ofwhich time the mixture appeared to be free flowing and exhibited notendency to spread resin dust. The mix thus prepared was used to maketest molds by the blowing process, and the resulting test cores had atensile strength of about 450 p.s.i.

Although the preferred compounds for use as coating agents have beendescribed above, other esters of phosphoric acid such as cresyl diphenylphosphate, diphenyl octyl phosphate, tri (p-tert-butyl phenyl)phosphate, triphenyl phosphate and diphenyl mono-o-xenyl phosphate.

Although the present invention has been described with a certain degreeof particularity, it is understood that the present disclosure has beenmade only by way of example, and that numerous changes in details ofcomposition and procedure may be resorted to without departing from thespirit and the scope of the invention as hereinafter claimed.

We claim:

1. A free flowing, blowable mold forming composition consistingessentially of a major proportion of sand, a minor proportion but atleast 1% of a powdered phenol formaldehyde thermosetting resin, and aliquid coating agent causing the resin to form a substantially uniformcoating about each sand particle after mixing, said coating agent beinga liquid which is an organic ester of phosphoric acid, the ratio of saidcoating agent to said resin being in the range of 1:10 to 4:10 byweight.

2. A free flowing, blowable mold forming composition consistingessentially of a major proportion of sand,

a minor proportion but at least 1% of a powdered phenol formaldehydethermosetting resin, and a liquid coating 10 mono-o-xenyl phosphate, theratio of said coating agent to said resin being in the range of 1:10 to4:10 by weight.

3. A composition as claimed in claim 1 in which the coating agent istricresyl phosphate.

4. A composition as claimed in claim 1 in which the coating agent istributyl phosphate.

5. A composition as claimed in claim 1 in which the coating agent istriethyl phosphate.

6. A composition as claimed in claim 1 in which the coating agent istriphenyl phosphate.

7. A composition as claimed in claim 1 in which the coating agent iscresyl diphenyl phosphate.

8. A free flowing, blowable mold forming composition consistingessentially of a major. proportion of sand, a minor proportion but atleast 1% of a powdered phenol formaldehyde thermosetting resin, and aliquid coating agent applied to the surface of the sand particles which,when admixed in a mechanical mixing device, causes the resin to form asubstantially uniform coating about each sand particle, said coatingagent being a liquid organic ester of phosphoric acid, having a boilingpoint greater than 100 C. and which, when mixed in a ratio of about 1:5and heated together with a reference novolac'resin having a meltingpoint of about C. by the shrink test, and when heated to a temperaturegreater than the melting point of the resin, forms a homogeneous mixturewith the resin, the melting point of which mixture is not more than 30C. below the melting point of the standard reference resin, the ratio ofsaid coating agent to said powdered thermosetting resin being in therange of 1:10 to 4: 10 by weight.

9. A process for producing a molding composition as claimed in claim 1wherein each sand particle is substantially coated with a uniformcoating of resin which comprises mixing together a major proportion ofsand and from 0.1% to 4% by weight of a coating agent which is anorganic ester of phosphoric acid, adding a minor proportion but at least1% of a powdered phenol formaldehyde thermosetting resin, the ratio ofsaid coating agent to said resin being in the range of from 1:10 to 4:10by weight, and continuing the mixing process until a substantiallyuniform coating of resin has formed on each 'sand particle.

References Cited in the file of this patent UNITED STATES PATENTS1,439,056 Baekland Dec. 19, 1922 1,856,371 Baldwin May 3, 1932 2,328,622Crawford Sept. 7, 1943 2,435,858 Whitehead Feb. 10, 1948 2,446,872Ehlers Aug. 10, 1948 2,521,614 Valyi Sept. 5, 1950

1. A FREE FLOWING, BLOWABLE MOLD FORMING COMPOSITION CONSISTINGESSENTIALLY OF A MAJOR PROPORTION OF SAND, A MINOR PROPORTION BUT ATLEAST 1% OF A POWDERED PHENOL FORMALDEHYDE THERMOSETTING RESIN, AND ALIQUID COATING AGENT CAUSING THE RESIN TO FORM A SUBSTANTIALLY UNIFORMCOATING ABOUT EACH SAND PARTICLE AFTER MIXING, SAID COATING AGENT BEINGA LIQUID WHICH IS AN ORGANIC ESTER OF PHOSPHORIC ACID, THE RATIO OF SAIDCOATING AGENT TO SAID RESIN BEING IN THE RANGE OF 1:10 TO 4:10 BYWEIGHT.